What is PGD?
PGD is a technique that enables couples with a particular inherited condition in their family to avoid passing it on to their children. The process helps potential parents prevent the birth of a child with a serious genetic condition. PGD is used when one or both parents has a known genetic abnormality and diagnostic testing is performed on an embryo to determine if it has also inherited the abnormality.
PGD involves the use of Assisted Reproductive Technology (ART). Eggs are obtained and fertilized through In Vitro Fertilisation (IVF). Once fertilized, the embryo develops for 2-3 days and then one or two cells are removed from each embryo. The genetic material (DNA or chromosomes) within each cell is then tested for the genetic or chromosomal abnormality. Up to two unaffected embryos are then transferred to the woman’s uterus to implant. If successful, the procedure will result in pregnancy and the child should not be affected by the condition for which it was tested.
The first successful birth of a “test tube baby”, Louise Brown, occurred in 1978. Louise Brown was born as a result of natural cycle IVF where no stimulation was made. Robert G. Edwards, the physiologist who developed the treatment, was awarded the Nobel Prize in Physiology or Medicine in 2010.
Couples who request PGD are at risk of passing on a serious genetic condition to their children. Parents may have these conditions themselves or be carriers of the conditions. They may already have a child affected with the genetic condition or they may have even experienced the loss of a child or pregnancy affected with the condition.
Carriers of a serious autosomal recessive condition :For carriers of an autosomal recessive condition, there is a 1 in 4 (25%) risk of each pregnancy delivering an affected child.
Carriers of a serious autosomal dominant condition :For carriers of an autosomal dominant condition, there is a 1 in 2 (50%) risk of each pregnancy delivering an affected child.
Couples with a family history of serious sex-linked disorders : Couples with a family history of a sex-linked disorder have a 1 in 4 (25%) risk of each pregnancy delivering an affected child (half of all male children).Therefore, PGD may be recommended if:
you or your partner has a family history of a serious genetic condition and/or
you and your partner already have a child with a serious genetic condition and/or
you and your partner have had a number of pregnancy terminations because your baby had a serious genetic condition.
For many genetic conditions, cures do not currently exist and are not likely to be found soon. Additionally, available treatments often carry substantial risks or have adverse effects. Even if effective, affordable treatment were guaranteed to be available, the psychological impact of late onset conditions on those at risk and on their families is significant. Therefore, the option of preventing the condition may be preferable to waiting for a possible cure to eventually become available.
An alternative to prenatal diagnostic testing :Couples avoid the distress associated with diagnosis, particularly if late in an established pregnancy, as well as the risk of miscarriage associated with such testing.
An alternative to termination of pregnancy : If prenatal testing (through amniocentesis or chorionic villus tests) reveals a genetic abnormality, the options available to parents are to have a child with a genetic condition or to undergo a pregnancy termination. This is a difficult and often traumatic decision. However, PGD is performed before pregnancy begins, thus eliminating these difficult decisions.
The opportunity to conceive a pregnancy that is biologically the parents’ own and yet unaffected by a genetic condition in the family:Couples for whom the option of prenatal testing and termination is not an acceptable choice are unlikely to want to take the risk of a child having a genetic condition. In the past, potential parents with a genetic condition or those who know that they are carriers frequently chose adoption, embryo donation, or surrogacy or chose not to have children in order to avoid the risk of passing on the condition. PGD now allows these couples the opportunity to have a child free of the condition.